Probably "quietly", if at all possible. Imperial Agents tend to try and deal with rumours of and evidence of the ancients without making a big public splash about it (see Secrets Of The Ancients).

325 ships (out of curiousity, why are all the values in your posts such oddly specific numbers?) is a big force, but if it's a mix of frigate-to-battleship ships it's a huge force but not necessarily armada-crushing; the big question will be what tech level they are.

If this putative super-empire has ships in commission between TL14 (at or slightly below Imperial 'front line' tech and TL25 ('tell physics to sit down and shut the hell up') then a pirate - even a successful one - could be anywhere on that scale, but probably at the lower end. After all, he was the one running away.

Whatever the imperium does with news that there's a ludicrously huge, super-powerful empire that's a vast distance away and doesn't plan to attack them any time soon doesn't really matter. What matters is the appearance of a pocket subsector fleet with (by imperial standards) cutting edge medium and heavy warships crewed by criminals just appeared in their back yard. That has to be dealt with, ideally without fixating public debate on where they came from.

Also, a fair point (depending on whether you include any ancients stuff, and especially any living ancients stuff) is how Grandfather and his brood might react to this empire. After all, it's essentially exactly what SEVEN was supposed to be preparing for (threat of invasion by hyper-advanced extra-galactic aliens). Some of them might try to investigate subtly. Others might react....not so subtly.

Understand that I'm not advocating violence.
I'm just saying that it's highly effective and I strongly recommend using it.

Size wise the pirate ships range from 3,800 tons TL 14 ships that are his races heaviest none-unique Scoutship design, but are comparable to A Medium Imperial Frigate to A 155,000 ton Ship that is his races heaviest none-unique Frigate design, is TL 18 and is comparable with A Very Light Imperial Battleship. Does that help.

PS. Only double checked my initial notes this morning, sorry about not posting 100% accurate notes several weeks back

Size wise the pirate ships range from 3,800 tons TL 14 ships that are his races heaviest none-unique Scoutship design, but are comparable to A Medium Imperial Frigate to A 155,000 ton Ship that is his races heaviest none-unique Frigate design, is TL 18 and is comparable with A Very Light Imperial Battleship. Does that help.

So....assuming it's mostly lighter ships, but a few capital vessels, you're looking at a force that's not something you can ignore, but is still a pretty significant threat. A subsector fleet mostly has light stuff like patrol cruisers and decommissioned front-line cruisers, so it'll be able to put up a fight against lighter stuff but not heavier stuff. A Sector Fleet ("proper" imperial navy") Batron will be able to turn his ships to junk, but that's essentially deploying major warfighting capital ships - something the Sector admiralty will be loath to do.

If he starts playing corsair again, then the Imperial Navy will have to hunt him down, but I can't see why or how he could plan to do that if he's sensible;
logically he can't have any local contacts, or facilities (movies aside, piracy only works if you have 'legitimate' business or governments willing to underwrite you) , and even if he's got the odd depot ship or two, it's not like he can seize useful parts for a TL15-ish ship (that I'd assume is the bulk of his force) from passing traders, or even, frankly, most subsector fleet ships.

At the same time, he won't have the firepower to stand off dreadnoughts if he gets cornered, nor the crew to man them if he can take them.

A lot will depend on what he intends to do. He's got priceless resources he can barter to major governments and megacorps - his technicians and the tech manuals for his ships - but can't afford to give up the ships themselves.

Did his one-shot-gate land him in charted space deliberately, or was it an "initiating getting the hell out of here maneuver" with an essentially random exit?

Understand that I'm not advocating violence.
I'm just saying that it's highly effective and I strongly recommend using it.

I like the idea that, in order throw off pursuit, he just had his flagships computer randomly pick a less advanced galaxy that was at least 440 years time at Jump 6 from his own races territory, ours was the 1 randomly picked, pressed fhe button to do it and hoped for the best

The Pirate's average TL's for his none-ship tehnology ranges from around 6.9 TL'S over The Imperiums average of TL 11.6, 3.1 TL's over The Imperiums best of 15.4 but 0.3 TL's below his races average of 18.8 and 6.97 TL's below his races best of TL 25.4. Does that help

The Imperium's "average" TL is not an easy thing to define.
The average imperial world may be TL11-12 or so, but the average imperial citizen lives on a multi-billion-person TL14-15 world (because the population of entire subsectors worth of thousand-to-million inhabitant worlds can vanish into one big core world). Equally, whilst system and subsector fleets have wildly varying tech levels, the Imperial Navy is pretty solidly nailed to TL14+.

The exact TL doesn't matter any more than the exact displacement of his ships; essentially Imperial Navy dreadnought BATRON formations can waste his ships, but will take extremely expensive losses doing so, because whilst he has a massive tech advantage, he is at a massive tonnage disadvantage, and has extremely limited options to make good damage or losses.

I like the idea that, in order throw off pursuit, he just had his flagships computer randomly pick a less advanced galaxy that was at least 440 years time at Jump 6 from his own races territory, ours was the 1 randomly picked, pressed fhe button to do it and hoped for the best

Right. So it's "run like hell" then, and he doesn't start with any contacts or specific resources that he didn't bring with him.

Equally, that means no-one will specifically know who he is, or that he's a pirate. Most likely, you're going to see a bidding war, drifting discretely in and out of actual war, between various polities trying to get their hands on his services, ships, personnel and databases.

Discovering that there's a massive super-empire out there is disconcerting, but there is basically naff all that the Imperium or consulate could do about, so it'll be largely ignored in favour of more immediate problems; the pirate's ships and data either needs to be in their hands only, in their hands as well as anyone elses, or in shattered wreckage that no-one gets (and dreadnoughts would be moved up to ensure this). This is potentially a 'Cuban missile crisis' negotiation.

Understand that I'm not advocating violence.
I'm just saying that it's highly effective and I strongly recommend using it.

I haven't though that far in front yet and am welcome to ideas and suggestions. He won't appear in my games for at least 3 to 5 real-life months or for at least 5 or 6 ingame years. The thing is I have never even attempted something this big before and am in well over my head, but my personal pride won't let me ask my more knowledgable friends for hints, tips and advise, so I am asking the, in my opinion, great minds on this great website

Anymore ideas. Please, I have given up on the idea of creating a entire new race and just plan to have this guy cause trouble and eventually have his race show up, blast his fleet to bits with A Squad of 2 Titan XL Class Battleships and backup(we are talking TL 25 massing 5,460,900 that is their heaviest none-unique ship and half a dozen 892,600 ton TL 23 Dreadnoughts that are the 1st 6 working prototypes of their new heaviest none unique light Dreadnought that their race send to to crush The Pirate as a diplomatic gesture to the pirates many and varied influential victims), before vanishing never to be seen again. Any ideas on how to handle his raids and the response to what their recordings show of the overkill fleet

On the subject of him not having the crew to operate/run/man Dreadnoughts, I like the idea that he may have enough spare TL 17 gear to bribe A Corrupt Navy Admiral to let him steal A Decommissoned Super-Light Dreadnought of around 200,000 tons and have enough TL 17 gear to trade to Theevs Pirate Lords for personnel to operate/run/man a ship that is both too primitive for his crew to easily run without training and too big for his forces to occupy without causing major staffing issues among his smaller ships

I also like the idea that he is half Nacarh(Uber-Races name and pronounced with A G, not A C)and half human from A 27,000 to 27,100 year old Human Colony transplanted by The Agents, is A Nacarh Navy Traitor(but unlike my versions Darokyn really is guilty whist my versions Darokyn took the blame for the actions of The 2nd born son of Tobias current Duke's father), was, at the time of his promotion, the only none pureblood Nacarh to be made A 3rd Class Admiral and his fleet choose their loyalty to him over The Empire they had sworn to serve

The uber races 10 greatest pirate warlords commanding 10,429 ships that range from 11,400 tons and TL 16 to 1.3 million tons and TL 22 show up and start causing havock. but the uber race says that in return for coping till they can send help they will gift the imperium 6 army surplus 800,000 ton TL 19 battleships and lift them to the very high end of TL 17

More thoughts and ideas please. I've been stuck for months and less then 46 minutes ago, as of writing this, swallowed by pride to admit it.

Also ideas for using them in 2nd edition Pirates of Drinax where corrupt officials swap Cr 100 billion in Drinax Treasure to do in 9.5 years what Adventure 7 says The GeDeCo would take at least 10 to 11 decades to do and them swapping techno wonders of Drinax for 8,000 to 18,200 ton TL 16 Ships, are very heavy escorts to them, but are very heavy to super heavy cruisers to The Imperium and are capable of destroying Aslan and Imperial Ships 2 to 3 times their size, but have been in museums for at least 2,800 to 3,100 years and that will net the officials at least 60.2% profit on the deal when they sell to collectors of tech that has been obsolete for between 3,500 and 4,200 years

Mainly for how to have The Pirates of Drinax being the 1's making 1st contact and them, Oleb and Drinax as a whole being manipulated for the uber-races benefit, but in a way that they think they are doing the manipulating for Drinax's benefit